1. Technical Field
The present invention relates to an electronic timepiece, specifically, a solar battery and a rechargeable battery being charged by the electricity generated by the solar battery.
2. Background Technology
In the past, it is known that the electronic timepiece includes a solar battery and a rechargeable battery, where electricity generated by the solar battery is charged in the rechargeable battery to drive the electronic timepiece (For example, refer to patent document 1). Generally, such solar battery includes a plurality of cells (electricity generating part).
By the way, in a case of an electronic timepiece that includes a rechargeable battery having a rechargeable structure, deterioration of the rechargeable battery progresses when the voltage supplied to the rechargeable battery exceeds a predetermined voltage. Therefore, a shortened life becomes an issue. In order to address this issue, there is an electronic timepiece that includes a feature for preventing the over-charging of the rechargeable battery (for example, refer to patent document 2).
The electronic timepiece disclosed in the patent document 2 includes; a rotating spindle that rotates according to the motion of the arm of user on which the electronic timepiece is worn; a gear such as rotating spindle gear in which the rotation of the rotating spindle is transferred; and an electricity generating device that generates electricity by the torque transferred by the gear. This electronic timepiece further includes a battery voltage detecting unit and a battery voltage control means. The battery voltage control means actuates a limiter to prevent supplying of the electricity generated by the electricity generating device to the rechargeable battery, when the voltage of the rechargeable battery detected by the battery voltage detecting means is higher than the predetermined value.
As just discussed, the electronic timepiece that includes a rechargeable battery having a rechargeable structure generally incorporates a over-charge prevention feature to prevent over charging of the rechargeable battery because voltage value of the charging current supplied, in compliance with the environment, to the rechargeable battery is unknown. In other words, voltage value of the electricity generating current by the electricity generating device is unknown.
Japanese Laid-open Patent Application No. 2004-279252 (Patent Document 1) and Japanese Laid-open Patent Application No. 2008-256453 (Patent Document 2) are examples of the related art.